This invention relates generally to a loom shaft comprising a heddle frame of upper and lower support bars, upper and lower heddle support rails attached to the support bars, a plurality of heddles lined up on the heddle support rails, and more particularly to a damping system for the heddles of the loom shaft permitting proper operation even at high weaving machine speeds and with loom shafts of traditional design.
Stress increases significantly on loom shafts with increased speed of the weaving machines. This has great impact on the heddles lined up on the heddle support rails of the loom shaft. In some instances conditions have now been reached in which traditional systems of shafts and heddles are no longer operationally satisfactory. It is, however, possible to manufacture the loom shafts at economically reasonable costs to withstand increases in mechanical stress. The standardized shape and tolerance between heddles and shafts or the elements of the shafts supporting the heddles, or the heddle support rails are such that a greater amount of wear occurs on the heddle support rails and the heddles themselves. After a very short time, this leads to failure of the heddles, for example, by breaking off at the end eyes. The shafts are often thereby damaged. In any case, production stops and faults in the woven textile occur as the result of such breaks in the heddles.
There are two approaches disclosed that offer a solution to the aforementioned problem. International application WO 97/26396 discloses the insertion of damping elements parallel to the heddle support rails and directly in contact with the heddle support rails. Although this solution is functional, the movability of the heddles is significantly restricted through the use of such damping elements. This leads to the fact that the heddles cannot easily keep up with the changing positions of the warp threads. Stripes in the warp are thus the unwanted result. Moreover, it is very difficult to mount heddles on the shafts and to repair broken warp threads since heddles must be thereby moved to do so.
Such disadvantages are also mentioned in German published application 199 62 977 disclosing the fastening of damping elements on the shaft in such a manner that the outer end of the heddles can make contact with such damping elements before the heddles are pulled by the heddle support rail. The drive for the heddle occurs then, according to such an approach, via the damping elements and not via the heddle support rails. However, it is extremely difficult to determine the appropriate spacing between the end of the heddle and the damping element. Since the heddles are no longer pulled by the heddle support rail as usual, but according to this prior art approach are pushed by the damping elements, the position of the heddle becomes unstable and they then have the tendency to turn sideways. This may be relatively harmless depending on the existing weaving conditions but it could possibly lead to unwanted stripes in the warp or the heddles might become wedged between the two heddle support rails of the shaft. The consequences are that the warp thread may break and oftentimes the heddles themselves may break as well.